Have a look at the Swift 8-32 front focus. It's light, good optics, and £189 from BAR. Alternatively the Bushnell 4200 8-32 can be had second hand for about £275. Very similar scope.

Sidewheel scopes are more common than front focus in FT but by and large they are heavier, bulkier, and more expensive. The Leupolds are lighter than many but again among the most expensive.

We have had juniors (age 14 and 15) in our club enjoying their shooting immensely and doing well enough to beat their fathers with better kit, using S200 rifles with Varmint 8-32 scopes that were remaindered at £80. The Swift or the Bushnell will be quite good enough until he is older and bigger. The very best of good luck to him.